Method for determining the position of a magnetic element using hall effect linear sensors and associated device

ABSTRACT

Method for determining the position of a magnetic element on a gearbox selector of an automobile, generating a magnetic field ({right arrow over (V)}), the speed selector moving in two directions with respect to a longitudinal axis, a main direction and a secondary direction, the magnetic element facing a position sensor including three Hall effect cells, includes measuring three voltages (V 1 , V 2 , V 3 ) at the respective outputs of the three Hall effect cells oriented in the same direction and positioned as follows: two cells being aligned on a transverse axis perpendicular to the longitudinal axis, the third cell being positioned on the longitudinal axis perpendicularly to the transverse axis, passing through the other two Hall effect cells,
         calculating a ratiometric ratio (P) between the first, second and third voltages defined by:       

     
       
         
           
             P 
             = 
             
               k 
               * 
               
                 ( 
                 
                   
                     
                       V 
                       3 
                     
                     + 
                     
                       
                         k 
                         1 
                       
                       * 
                       V 
                     
                   
                   
                     V 
                     + 
                     
                       
                         k 
                         3 
                       
                       * 
                       
                         V 
                         3 
                       
                     
                   
                 
                 ) 
               
             
           
         
       
         
         
           
             
               
                 with V=√{square root over (V 1   2 +V 2   2 )} and k, k 1 , and k 3  being constants, 
               
             
             deducing the position of the magnetic element in the secondary direction.

The present invention relates to a method for determining the positionof a magnetic element using linear Hall effect position sensors. Theinvention also relates to the device allowing this method to beimplemented.

More particularly, the invention is applicable to the detection of theposition of a gearbox selector of an automobile vehicle and allows thegear ratio which is selected by the driver to be determined.

The selection of a gear ratio for an automobile vehicle is generallycarried out, for a manual gearbox, by a gear stick situated in thepassenger compartment of the vehicle which, by means of a transmissionlinkage connected to an axis for selection of the gearbox ratio, allowsa gear ratio to be selected in the gearbox by various systems of gears,known to those skilled in the art and not detailed here. The latter isgenerally situated under the vehicle and connected to the wheels and tothe engine.

The gear stick can move in two perpendicular directions. This example islimited to the case of a gearbox comprising six gear ratios: 1^(st),2^(nd), 3^(rd), 4^(th), 5^(th) gears and reverse gear R (cf. FIG. 2).“Speed of the vehicle” will refer to the gear ratio selected in thegearbox and “neutral” N the null gear ratio. The movement of the gearstick is transmitted, in the gearbox to the speed selection axis, alsoreferred to as speed selector, which itself moves in translation and inrotation relative to the longitudinal axis of the gearbox. By means ofvarious mechanical gears, this translational and rotational movement ofthe speed selector allows the speed chosen by the driver to be engaged.

In order to perform certain functions of the vehicle, such as forexample turn off the engine when the gearbox is in neutral in order toreduce polluting emissions, it is common to use a sensor for theposition of the speed selector. This position sensor generally comprisesa linear Hall effect cell, connected to an integrated electroniccircuit. A linear Hall effect cell is understood to mean an element,made of conducting or semiconductor material, through which a currentflows and which is subjected to a magnetic field perpendicular to thiscurrent, which produces an output voltage proportional to the magneticfield and to the current flowing through it. The measurement plane ofthe Hall effect cell is perpendicular to the magnetic field generated bythe magnetic element. A linear Hall effect cell will be referred to asHall effect cell in the following part of the description.

As illustrated in FIG. 1, the position sensor 60 is generally situatedin the housing 10 of the gearbox 30, facing a magnetic element 50situated on the speed selector 20 (by means of a support 40) whichmoves, when the speeds are selected, in rotation in the main directionZ, and in translation in the secondary direction X, with respect to thelongitudinal axis A of the gearbox 30. The magnetic element 50 isoriented in such a manner that it creates a magnetic field {right arrowover (V)} which varies with the direction of movement of the speedselector 20 that it is desired to detect. In FIG. 1, the magnetic field{right arrow over (V)} is oriented perpendicularly to the longitudinalaxis A, and transversely with respect to the speed selector 20, in orderto measure the rotational movement in the main direction Z of the speedselector 20. The orientation of the magnetic field {right arrow over(V)} is illustrated more clearly in FIG. 2 which shows a top view ofFIG. 1. The magnetic field {right arrow over (V)} y is oriented alongthe transverse axis B of the gearbox 30. A Hall effect cell 70 detectsthe variations in the magnetic field {right arrow over (V)} induced bythe translational movement or in rotation (as in the example illustratedin FIG. 1) of the magnetic element 50 and thus determines the positionof the speed selector 20.

However, this detection can only be carried out in a direction ofmovement of the speed selector 20, the Hall effect cell 70 only beingsensitive to a direction of the magnetic field {right arrow over (V)}generated by the magnetic element 50. In order to detect whether thegear stick 80 is, for example, in neutral N, the Hall effect cell 70 andthe magnetic element 50 are positioned for determining the rotationalposition, in the main direction Z, of the speed selector 20. Aspreviously explained and illustrated in FIG. 2, the magnetic field{right arrow over (V)} created by the magnetic element 50 and detectedby the position sensor 60 is oriented along the transverse axis B of thegearbox 30. If the speed selector 20 rotates in the positive sense, inthe main direction Z, this means that one of the even speeds (2^(nd) or4^(th) gear) or reverse gear R is selected by the gear stick 80. If itrotates in the opposing sense, in other words negative, one of the oddspeeds is selected (1^(st), 3^(rd) or 5^(th) gear), and finally, if itis centered on the longitudinal axis A, then the gear stick 80 isconsidered to be in neutral.

As illustrated in FIG. 2, in order to overcome the drifts in themagnetic element and also the variations in the distance between themagnetic element and the position sensor 60, it is common to use aratiometric ratio between the output voltages of two Hall effect cells70 a and 70 b, situated within a single position sensor 60. These Halleffect cells 70 a and 70 b are situated in the same measurement plane,in other words they are coplanar in the plane defined by thelongitudinal axis A and the transverse axis B, and they measure the samemagnetic field {right arrow over (V)}. Indeed, by using a ratiometricratio between the output voltages of two Hall cells 70 a, 70 b, thiseffect is cancelled. This method is, for example, described in thedocument FR 2 926 881. In this document FR 2 926 881, the arctangent ofthe ratiometric ratio between the output voltages of two Hall cells isused in order to detect the position of the speed selector 20 inrotation, hence independently of certain variations.

At the present time, this detection along a single direction of movementis insufficient, and it is useful to be able to detect the speedselected precisely in order to improve the performance characteristicsof the vehicle (noise, emissions) by anticipating for example the changein speed. It therefore becomes necessary to be able to detect not onlythe type of speed selected (even, odd, neutral), but also the actualspeed, and hence to detect the movement of the speed selector 20 in thetwo directions of movement, in rotation and in translation, with respectto the longitudinal axis A of the gearbox.

For this purpose, it is usual to add (cf. FIG. 3) an additional magneticelement 500 on the speed selector 20, oriented in such a manner that itcreates a magnetic field {right arrow over (V)}₂ in the second directionof movement, or secondary direction X, that it is desired to detect (inour example, the translation), together with a position sensor 600situated facing the latter (for example on the housing 10 of the gearbox30) comprising one or two Hall cells 700 a and 700 b. These are situatedin the same measurement plane and oriented so as to measure this secondmagnetic field {right arrow over (V)}₂. These two Hall effect cells 700a and 700 b thus each produce an output voltage proportional to themovement of the speed selector 20, in this case in translation, in thepositive direction of the secondary direction X. This configuration(using a single Hall effect cell per sensor) is described in thedocument WO 97 46 815. By using two magnetic elements 50 and 500 and twoposition sensors 60 and 600 (each comprising one or two Hall effectcells), in other words by duplicating the device used to detect themovement of the speed selector 20 in one direction only, it is thereforepossible to detect its movement in the two directions and hence toprecisely determine the speed selected by the user via the gear stick.This solution is robust but costly, since it is necessary to add amagnetic element and a position sensor.

The aim of the invention is therefore to provide a method fordetermining the position of the speed selector in the translational androtational directions using a lower cost device than that of the priorart.

The aims of the invention are achieved by means of a method fordetermining the position of a magnetic element, situated on a gearboxselector of an automobile vehicle, generating a magnetic field {rightarrow over (V)}, said selector moving in two directions with respect toa longitudinal axis, a main direction of rotation about the longitudinalaxis and a secondary direction of translation along the longitudinalaxis, the magnetic element being situated facing a position sensorcomprising three Hall effect cells, the method consisting in measuring afirst voltage, a second voltage and a third voltage at the respectiveoutputs of a first Hall effect cell, of a second Hall effect cell and ofa third Hall effect cell. The invention is noteworthy in that the threeHall effect cells are oriented in the same direction for measuring themagnetic field {right arrow over (V)}, and are positioned in thefollowing manner:

-   -   two Hall effect cells are aligned on a transverse axis        perpendicular to the longitudinal axis of the speed selector and        have a first gap between them along the transverse axis,    -   the third Hall effect cell is positioned on the longitudinal        axis, in other words perpendicularly to the transverse axis,        passing through the other two Hall effect cells, and has a        second gap along the longitudinal axis with respect to the        position on this axis of the other two cells.        Said method furthermore comprises:    -   a step consisting in calculating a ratiometric ratio P between        the first voltage V₁, second voltage V₂ and third voltage V₃, in        order to deduce from this the position of the magnetic element        in the secondary direction of movement of the gearbox selector.    -   The ratiometric ratio P between the first voltage V₁, second        voltage V₂ and third voltage V₃ is defined in the following        manner:

$P = {k*\left( \frac{V_{3} + {k_{1}*V}}{V + {k_{3}*V_{3}}} \right)}$

-   -   -   with V=√{square root over (V₁ ²+V₂ ²)}, the geometric mean            between the first voltage V₁ and second voltage V₂. and k,            k₁, and k₃ being constants.

    -   a step consisting in deducing the position of the magnetic        element in the secondary direction of movement of the gearbox        selector, the ratio P varying linearly with the position of the        magnetic element in the secondary direction of movement of the        gearbox selector.        Advantageously, three Hall effect cells are used that are        coplanar in a plane defined by the longitudinal and transverse        axes.

In one preferred embodiment, the precise determination of the positionof the speed selector can be carried out by choosing k=1, k₁=0 and k₃=0,in other words using a simplified expression for the ratiometric ratioP:

$P = \frac{V_{3}}{V}$

A key idea of the invention is to linearize the geometric mean V betweenthe first voltage V₁ and second voltage V₂ in order to avoid anypotential fluctuations in the values of the ratiometric ratio P due tothe rotation of the magnetic element and in order to obtain a bettercorrelation between the values of the ratiometric ratio P and the valuesof the movement of the speed selector.

In one variant embodiment, and advantageously, said method furthermorecomprises a preliminary step consisting in setting the design parametersof at least one of the following elements:

-   -   dimensions of the magnetic element,    -   gap along the longitudinal axis and the transverse axis between        each of the three Hall effect cells,    -   gap along the longitudinal axis and the transverse axis between        the magnetic element and the measurement plane of the Hall        effect cells,        according to a law of variation of the voltage measured at the        output of each Hall effect cell, itself a function of the        position of the magnetic element with respect to said Hall        effect cell, in order to obtain the desired precision on the        detection of the speed engaged.

Alternatively, and in order to simplify the aforementioned designparameter setting, the idea of the invention is to use identical Halleffect cells.

In a first embodiment and according to the typical configuration of agearbox for a front-wheel-drive vehicle, the main direction of movementis that of the rotation of the speed selector about the longitudinalaxis, and the secondary direction is the translation of the speedselector along the longitudinal axis.

In a second embodiment, and according to the typical configuration of agearbox of a rear-drive vehicle, the main direction of movement is thatof the translation of the speed selector along the longitudinal axis andthe secondary direction is the rotation of the speed selector about thelongitudinal axis.

In one preferred embodiment, the method comprises a preliminary stepconsisting in calculating the arctangent of the ratio between the firstvoltage and the second voltage in order to deduce from this the positionof the magnetic element in the main direction of movement of the gearboxselector, in other words in the direction of rotation along thelongitudinal axis.

The invention also provides a device for determining the position of amagnetic element situated on a gearbox selector of an automobile vehicleallowing the method described hereinabove to be implemented.

The invention also relates to any associated gearbox selector positionsensor.

Other advantages, aims and features of the invention will becomeapparent upon reading the description that follows, presented by way ofnon-limiting example, and upon examining the appended drawings in which:

FIG. 1 shows a partial schematic view of a gearbox equipped with aposition sensor according to the prior art,

FIG. 2 shows a partial schematic top view of a gearbox equipped with aposition sensor according to FIG. 1,

FIG. 3 is a partial schematic view of a gearbox equipped with twoposition sensors according to the prior art,

FIG. 4 is a partial schematic view of a gearbox equipped with a positionsensor according to the invention,

FIGS. 5 and 6 are graphical representations of the measurements of thepositioning of the speed selector according to the invention.

FIGS. 1, 2 and 3 show devices of the prior art and have been detailedpreviously.

As illustrated in FIG. 4, according to the invention, the positionsensor 60 comprises three Hall effect cells 70 a, 70 b, and 70 c, alloriented in the same direction (for example in the South-Northdirection, see arrow S->N in FIG. 4). These each supply an outputvoltage (V₁, V₂ and V₃, respectively) proportional to the intensity ofthe magnetic field that they measure, which magnetic field is created bythe magnetic element 50 situated on the speed selector 20, facing theposition sensor 60.

According to one preferred embodiment (cf. FIG. 4), the Hall effectcells 70 a, 70 b, 70 c are coplanar, in a plane defined by thelongitudinal axis A and the transverse axis B, and positioned in such amanner that the two cells 70 a, 70 b are aligned on the transverse axisB perpendicular to the longitudinal axis A of the speed selector 20. Thetwo cells 70 a, 70 b have a first gap e1 between them along thistransverse axis B. The third Hall effect cell 70 c is positioned on thelongitudinal axis A, in other words perpendicularly to the transverseaxis B, passing through the other two Hall effect cells 70 a, 70 b. Thethird Hall effect cell 70 c has a second gap e2 on the longitudinal axisA with respect to the position of the other two cells 70 a, 70 b on thisaxis. In this configuration, the output voltages produced by the firstHall effect cell 70 a and the second Hall effect cell 70 b (V₁ and V₂,respectively) are two sinusoids the arctangent of whose ratio allows therotational position of the magnetic element 50 to be determined (cf.FIG. 5). This is known from the prior art and has been explainedpreviously.

In FIG. 5, the abscissa axis shows the value in degrees of the rotationof the speed selector 20 in the main direction Z, and the ordinate axisshows the value of the output voltage supplied by the Hall effect cells70 a and 70 b. The output voltages of the first Hall cell 70 a and ofthe second Hall cell 70 b, in other words V₁ and V₂, are thereforerepresented in the form of sinusoids and the arctangent of the ratio ofthese two voltages, Q, is represented in the form of a straight linewhose values are proportional to the rotational movement of the magneticelement 50 in the main direction Z.

The invention furthermore uses the geometric mean V of these twovoltages V₁ and V₂, defined by:

V=√{square root over (V ₁ ² +V ₂ ²)}  (1)

together with the output voltage V₃ of the third Hall effect cell 70 c,in order to determine the translational position in the secondarydirection X of the speed selector.

As illustrated in FIG. 5, this geometric mean V is practicallyinsensitive to the rotational movement in the main direction Z of themagnetic element 50. By using this feature and by dividing the outputvoltage of the third Hall effect cell V₃ by this geometric mean V, aratiometric ratio P is obtained which varies almost linearly with thetranslational movement in the secondary direction X of the magneticelement 50. The ratiometric ratio P is therefore defined by:

$\begin{matrix}{P = \frac{V_{3}}{V}} & (2)\end{matrix}$

In FIG. 6, the abscissa axis represents the value of the translationalmovement in the secondary direction X of the magnetic element 50, andthe ordinate axis represents the value of the ratiometric ratio P. It isclearly apparent that the curve representing the ratiometric ratio Pcorresponds to a straight line, whose values are proportional to thetranslational movement of the magnetic element 50 in the secondarydirection X. This straight line therefore allows the translationalmovement effected by the magnetic element 50 to be directly determinedfor each value of P.

The ratiometric ratio P can be generalized and defined in the followingmanner:

$\begin{matrix}{P = {k*\left( \frac{V_{3} + {k_{1}*V}}{V + {k_{3}*V_{3}}} \right)}} & (3)\end{matrix}$

with k, k₁ and k₃ being constants.

Indeed, for any value of k, k₁ and k₃, the ratiometric ratio P isrepresented by a straight line whose values are proportional to thetranslational movement in the secondary direction X of the magneticelement 50. The user can thus choose the values of k, k₁ and k₃ in orderto obtain the desired measurement precision, depending on the embodimentenvisioned. This adjustment allows the user to compensate for the designparameter tolerances of the various elements of this device (size,positioning of the magnet for example), or the separations between theposition sensor 60 and the magnetic element 50, or again the measurementtolerances of the Hall effect cells 70 a, 70 b, 70 c.

Thus, the key addition of a third Hall effect cell 70 c within the sameposition sensor 60 as that used for determining the rotational movementof the speed selector 20 then allows the translational movement of thespeed selector 20 to also be determined. It is therefore no longernecessary to include an additional sensor 600 within the housing 10 ofthe gearbox 30, equipped with one or two Hall effect cells, togetherwith a second magnetic element 500, in order to perform thisdetermination, as was the case in the prior art.

Advantageously, the idea of the invention is to linearize the geometricmean V in order to obtain a ratiometric ratio P having a bettercorrelation with respect to the movement of the magnetic element 50.This linearization can be effected in a simple manner such as forexample by using a moving average or a correction table.

Of course, the positioning of the magnetic element 50 with regards tothe position sensor 60, together with the location of the Hall effectcells 70 a, 70 b, 70 c within the latter, affects the precision ofdetermination of the translational movement of the speed selector 20 inthe secondary direction X. Consequently, an improvement of the inventionconsists in setting design parameters for each of following elements,prior to the calculation of the ratiometric ratio P:

-   -   dimensions of the magnetic element 50,    -   gaps e1 and e2, along the longitudinal axis A and transverse        axis B, between each of the three Hall effect cells 70 a, 70 b,        70 c,    -   orientation, along the longitudinal axis A and transverse axis        B, of each of the Hall effect cells 70 a, 70 b, 70 c,    -   gap between the magnetic element 50 and the measurement plane of        the Hall effect cells 70 a, 70 b, 70 c,        according to a law of variation of the voltage measured at the        output of each Hall effect cell 70 a, 70 b, 70 c, which itself        is a function of the position of the magnetic element 50 with        respect to said Hall effect cell.

This setting of the design parameters thus allows the user to obtain thedesired measurement precision.

The method, according to the invention therefore allows the position ofa magnetic element 50, situated on a gearbox selector 20 of anautomobile vehicle, to be determined, said method comprising:

-   -   the use of three Hall effect cells 7 a, 70 b, 70 c situated        within the position sensor 60 and measuring, in the same        direction, the magnetic field {right arrow over (V)} generated        by the magnetic element 50, disposed in such a manner that two        cells are spaced out over the same transverse axis and the third        cell is spaced from the other two along the longitudinal axis,        said method furthermore comprising:    -   a step consisting in calculating a ratiometric ratio P between        the first voltage V₁, second voltage V₂ and third voltage V₃        measured at the respective outputs of the first Hall effect cell        70 a, second Hall effect cell 70 b and third Hall effect cell 70        c,    -   a step consisting in deducing the position of the magnetic        element in the secondary direction of movement of the gearbox        selector, the ratio P varying linearly with the position of the        magnetic element in the secondary direction of movement of the        gearbox selector.

It is of course possible to use three identical Hall effect cells 70 a,70 b, 70 c in order to simplify the aforementioned design parametersetting.

The invention can be implemented by using Hall effect cells 70 a, 70 b,70 c situated within the same position sensor 60, but non-coplanar.Similarly, the configuration of these Hall effect cells 70 a, 70 b, 70c, within the position sensor 60, along the longitudinal axis A and thetransverse axis B, can be arbitrary, as long as they measure themagnetic field {right arrow over (V)} in the same direction, in otherwords they are oriented in the same direction and they supply an outputvoltage proportional to the intensity of this magnetic field {rightarrow over (V)}. As previously explained, the choice of the constants k,k₁ and k₃ allows the user to adapt the ratiometric ratio P in order toobtain the desired precision independently of the position of the Halleffect cells 70 a, 70 b, and 70 c within the position sensor 60.

It should be noted that this method is applicable to both gearboxes 30of front-wheel-drive vehicles and to gearboxes 30 of rear-drivevehicles. The difference between these two types of gearboxes 30 residesin the orientation of the directions of movement of the speed selector.Thus, the main direction and the secondary direction of movement arereversed, and in the case of a gearbox of a rear-drive vehicle, the maindirection of movement is the translation and the secondary direction isthe rotation of the speed selector 20.

Embodiments of the invention may also be considered comprising a gearbox30 having more or less than six speeds. The invention is of courseapplicable to any configuration or type of gearbox (mechanical,automatic, automated, etc.).

It goes without saying that the invention is not limited to theembodiment described and shown which has only been presented by way ofexample.

1. A method for determining the position of a magnetic element (50),situated on a gearbox selector (20) of an automobile vehicle, generatinga magnetic field ({right arrow over (V)}), said speed selector (20)moving in two directions with respect to a longitudinal axis (A), a maindirection (Z) and a secondary direction (X), the magnetic element (50)being situated facing a position sensor (60) comprising three Halleffect cells (70 a, 70 b, 70 c), the method consisting in measuring afirst voltage (V₁), a second voltage (V₂) and a third voltage (V₃) atthe respective outputs of a first Hall effect cell (70 a), of a secondHall effect cell (70 b) and of a third Hall effect cell (70 c), saidmethod being characterized in that it comprises the use of three Halleffect cells (7 a, 70 b, 70 c) oriented in the same direction formeasuring the magnetic field ({right arrow over (V)}) and positioned inthe following manner: two Hall effect cells (70 a, 70 b) are aligned ona transverse axis (B) perpendicular to the longitudinal axis (A) of thespeed selector (20) and have a first gap (e1) between them along thetransverse axis, (B) the third Hall effect cell (70 c) is positioned onthe longitudinal axis (A), in other words perpendicularly to thetransverse axis (B), passing through the other two Hall effect cells,and has a second gap (e2) along the longitudinal axis (A) with respectto the position of the first two cells (70 a, 70 b) on this longitudinalaxis (A), and in that said method furthermore comprises: a stepconsisting in calculating a ratiometric ratio (P) between the firstvoltage (V1), second voltage (V2) and third voltage (V3) defined by:$P = {k*\left( \frac{V_{3} + {k_{1}*V}}{V + {k_{3}*V_{3}}} \right)}$with V=√{square root over (V₁ ²+V₂ ²)}, the geometric mean between thefirst voltage (V₁) and second voltage (V₂) and k, k₁, and k₃ beingconstants associated with the design parameters of the position sensor(60), a step consisting in deducing the position of the magnetic element(50) in the secondary direction (X) of movement of the selector (20) ofthe gearbox (30), the ratio P varying linearly with the position of themagnetic element (50) in the secondary direction (X) of movement of theselector (20) of the gearbox (30).
 2. The method as claimed in claim 1,characterized in that the three Hall effect cells (70 a, 70 b, 70 c) arecoplanar in a plane defined by the longitudinal axis (A) and transversal(B).
 3. The method as claimed in claim 1, characterized in that k=1,k₁=0 and k₃=0, and that the ratiometric ratio P is expressed:$P = \frac{V_{3}}{V}$
 4. The method as claimed in claim 2 characterizedin that the geometric mean (V) between the first measured voltage (V1)and second measured voltage (V2) is linearized.
 5. The method as claimedin claim 1, characterized in that said method furthermore comprises apreliminary step consisting in setting the design parameters of at leastone of the following elements: dimensions of the magnetic element (50),gap (e1, e2) along the longitudinal axis (A) and the transverse axis(B), between each of the three Hall effect cells (70 a, 70 b, 70 c),gap, along the longitudinal axis (A) and the transverse axis (B),between the magnetic element (50) and the measurement plane of the Halleffect cells (70 a, 70 b, 70 c), according to a law of variation of thevoltage measured at the output of each Hall effect cell (70 a, 70 b, 70c), itself a function of the position of the magnetic element (50) withrespect to said Hall effect cell (70 a, 70 b, 70 c).
 6. The method asclaimed in claim 1, characterized in that identical Hall effect cells(70 a, 70 b, 70 c) are used,
 7. The method as claimed in claim 1,characterized in that the main direction (Z) is that of the rotation ofa magnetic element (50) about the longitudinal axis (A).
 8. The methodas claimed in claim 7, characterized in that the secondary direction (X)is that of the translation of the magnetic element (50) along thelongitudinal axis (A).
 9. The method as claimed in claim 1 characterizedin that the main direction (Z) is that of the translation of themagnetic element (50) along the longitudinal axis (A).
 10. The method asclaimed in claim 9, characterized in that the secondary direction (X) isthat of the rotation of the magnetic element (50) about the longitudinalaxis (A).
 11. The method as claimed in claim 1, characterized in that itcomprises a preliminary step consisting in calculating the arctangent ofthe ratio (Q) between the first voltage (V1) and the second voltage (V2)in order to deduce from this the position of the magnetic element (50)in the main direction (Z) of movement of the selector (20) of thegearbox (30).
 12. A device for determining the position of a magneticelement (50) situated on a gearbox selector (20) of an automobilevehicle, generating a magnetic field ({right arrow over (V)}), saidspeed selector (20) moving in two directions with respect to alongitudinal axis (A), a main direction (Z) and a secondary direction(X), the magnetic element (50) being situated facing a position sensor(60) comprising three Hall effect cells (70 a, 70 b, 70 c), the devicecomprising means for measurement of a first voltage (V1), of a secondvoltage (V2) and of a third voltage (V3) at the respective outputs of afirst Hall effect cell (70 a), of a second Hall effect cell (70 b) andof a third Hall effect cell (70 c), said device being characterized inthat the three Hall effect cells (70 a, 70 b, 70 c) are oriented in thesame direction and measure the magnetic field ({right arrow over (V)})in the same direction and are positioned in the following manner: twoHall effect cells (70 a, 70 b) are aligned on a transverse axis (B)perpendicular to the longitudinal axis (A) of the speed selector (20)and have a first gap (e1) between them along the transverse axis (B) thethird Hall effect cell (70 c) is positioned on the longitudinal axis(A), in other words perpendicularly to the transverse axis (B), passingthrough the other two Hall effect cells, and has a second gap (e2) alongthe longitudinal axis (A) with respect to the position of the first twocells (70 a, 70 b) on this longitudinal axis (A), and in that saiddevice furthermore comprises: means for calculating a ratiometric ratio(P) between the first voltage (V1), second voltage (V2) and thirdvoltage (V3) defined by:$P = {k*\left( \frac{V_{3} + {k_{1}*V}}{V + {k_{3}*V_{3}}} \right)}$with V=√{square root over (V₁ ²+V₂ ²)}, the geometric mean between thefirst voltage (V₁) and second voltage (V₂) and k, k₁, and k₃ beingconstants associated with the design parameters of the position sensor(60), means for deducing the position of the magnetic element (50) inthe secondary direction (X) of movement of the selector (20) of thegearbox (30), the ratio P varying linearly with the position of themagnetic element (50) in the secondary direction (X) of movement of theselector (20) for the gearbox (30).
 13. The position sensor (60) for thegearbox selector (20) of an automobile vehicle implementing the methodas claimed in claim 1.